1. Field of the Invention
The present invention relates to an image processing apparatus for printing an image signal consisting of a number of horizontal scanning lines.
2. Description of the Prior Art
FIG. 1 shows a diagram for explaining the concept of the sampling of a television video signal in a conventional image processing apparatus of this kind. l.sub.1 to l.sub.n denote horizontal scanning lines and n=525 in the case of an NTSC signal. The first sampling point is at the left end of the first effective horizontal scanning interval. S.sub.1 to S.sub.n indicate sampling points and the sampling is sequentially performed on a line by line basis for one horizontal period in the vertical scanning direction. After completion of the sampling of one frame, a similar operation is then executed starting at sampling point S.sub.n+1 shifted in the horizontal direction by only a constant time t.
Now, in the case where the television video information, sampled as described above, is printed by making one sample point correspond to one dot, the signal process may be performed without executing the interpolating operation. However, for instance, as shown in FIG. 2, in the case of forming the print image which is 4/3 times larger than the original image, in order to obtain density information S.sub.m to S.sub.m+4 as shown in FIG. 2B that is 4/3 times larger than the original information from sample information S.sub.k to S.sub.k+3 shown in FIG. 2A, the linear interpolations as shown below, for example, are performed. EQU S.sub.m =S.sub.k EQU S.sub.m+1 =(2S.sub.k +S.sub.k+1)/3 EQU S.sub.m+2 =(S.sub.k+1 +S.sub.k+2)/2 EQU S.sub.m+3 =(S.sub.k+2 +S.sub.k+3)/3 EQU S.sub.m+4 =S.sub.k+3
By executing the above interpolation, even in the case where the print size was enlarged 4/3 times as shown in FIG. 2C, the interpolated information is derived from the original sample image due to the weighting; therefore, the vertical resolution does not deteriorate.
FIG. 3 is a block diagram of a signal processing system of a conventional video printer provided with an enlarging function to accomplish the foregoing function. A composite television video signal (e.g., NTSC signal) inputted from a terminal O is divided into three primary chrominance signals R, G and B by a decoder 1.
The respective chrominance signals obtained in this way are supplied to sample and hold circuits 2, 3 and 4, by which they are sampled at predetermined times. Thereafter, these sampling signals are digitized by A/D converters 5, 6 and 7. These digital signals are stored in one-line memories 8, 9 and 10 in the vertical direction, respectively. Each of the outputs of those memories is inputted to an input terminal of respective change-over switches 14, 15 and 16 and to respective interpolation circuits 11, 12 and 13. The linear interpolations as described in FIG. 2 are performed in these interpolating circuits. Outputs of the interpolation circuits 11, 12 and 13 are supplied to the other input terminals of the change-over switches 14, 15 and 16. In case of a standard size whereby the sampling point unconditionally corresponds to the print point to satisfy the relation of 1:1, those change-over switches are switched to the side of terminals A in response to an output of a print size setting circuit 19, thereby allowing the data of the line memories 8, 9 and 10 to pass. On the other hand, in the case of the enlargement size that is 4/3 times larger than the original size whereby there is the corespondence relation of 3:4 between the sampling point and the print point, the change-over switches are switched to the side of terminals B, thereby permitting the outputs of the interpolation circuits 11, 12 and 13 to pass, respectively.
Each image sampling data which is outputted from the change-over switches 14, 15 and 16 is supplied to an image processing circuit 17, by which it is subjected to gamma correction, masking process, etc. and is finally inputted as an input signal to a printer 18, so that it is printed.
On the other hand, a sampling signal to control the sample and hold circuits 2, 3 and 4 is formed by a sampling signal forming circuit 23. A preset value setting counter 22 is reset by an A/D start signal and counts fv/2, namely, the number of frames. As shown in FIG. 1 also, in this case, the constant timing from the left end of the effective scanning line to the time when the sampling is performed is set in accordance with this number of frames. The preset value which has been set in this way is loaded into a presettable counter 21 by a horizontal sync signal HD. The counter 21 uses, as a clock input, an output of an oscillator 20 which oscillates at a constant frequency. The counter 21 subtracts the foregoing loaded preset value in response to this clock signal and when the count value becomes 0 (zero), it generates the sampling signal by the borrow BO.
An example of the television signal as the NTSC signal has been described in the above. However, in this case, the number of sampling points in the vertical direction becomes the same as the number of effective vertical intervals, namely, 525.times.0.91.apprxeq.480, while the number of horizontal sampling points becomes 480.times.4/3=640 in consideration of the aspect ratio of the screen. In the case of enlarging the print size 4/3 times, the number of vertical samples becomes 480.times.4/3=640 and the number of horizontal samples becomes 630.times.4/3=853.
Considering a CCIR signal, the number of effective vertical scanning lines becomes 625.times.0.91.apprxeq.570 and the number of horizontal sampling points likewise becomes 570.times.4/3=760. In this case, when an image is enlarged 4/3 times by use of the interpolating method employed in the foregoing conventional embodiment, the number of vertical sampling points becomes 760 and the number of horizontal sampling points becomes 1012, so that the print size becomes fairly large as compared with the case of the NTSC signal. Therefore, if this apparatus were to be used for both NTSC and CCIR signals, a large blank portion, would result in the case where the NTSC signal is printed, causing a drawback such that the cost becomes comparatively high.
On the other hand, if a print paper size which gives a priority to the NTSC signal is used to avoid such an increase in cost, in the case of the CCIR signal, the enlargement of 4/3 times becomes impossible, even though it is effective in case of the standard size.
In addition, in the case of merely obtaining the image of double size from the NTSC signal as well, the number of sampling points in the horizontal scanning direction becomes 1280, so that if the image is to have the same density, it cannot be fully recorded on the recording paper.